Power systems with parallel-inputs and parallel-output configurations are used to provide electrical power using DC-to-DC power converters. In such systems, uniform current distribution control is solved by using manufacturer-provided parallel control ports with user-developed shared-bus control topology. Using shared-bus configurations, a control voltage commands the parallel-connected converters to operate as voltage-controlled current-sources, that is, as current mode converters where each converters is controlled as a voltage controlled current source. The current-mode and shared-bus approach to uniform current distribution is well known, particularly for parallel-input parallel-output connected power converters.
Another conventional practice in power systems, is to used the DC-to-DC converters in parallel-connected configurations where the converters are specified to be identical for uniform power distribution amongst the converters. In stand-alone configurations, the converters are often connected to the same input voltage source while the outputs of the converters independently distribute output voltages to individual loads. One problem with stand-alone converters is that internal component variations result in undesirable non-uniform output voltage distribution despite the parallel connection of the converters to the same input voltage source. The stand-alone converters need to have electrical isolation between the converter inputs and outputs to enable the outputs to be series connected. When these stand-alone converters are connected in a parallel-input and series-output configuration, non-uniformity in the output voltages of the converters results with uneven power distribution such that some converters may be overstressed while the remaining converters are not. Uneven distributed voltages can cause the converters to lose stability and can cause one or more of the converters to deliver an excessive portion of the output power across a common load. With excessive uneven power distribution, system reliability degrades mostly due to the result of thermal overstress to the converters that contribute a greater portion of the output power. Connecting the outputs of the converters in series cannot avoid uneven power distribution. Uneven power distribution occurs as a result of internal component mismatches among the series-output connected converters. The problems associated with non-uniform power distribution are not entirely eliminated even with external controls that conventionally do not have dedicated closed-loop regulation for output voltage distribution.
When parallel-input series-output converters are operated in a current mode, mismatches in component values can still lead to uneven power distribution as well as different modes of operations. Among the nearly identical parallel-input and series-output connected converters, some converters may operate in over-current protection mode and some converters in normal output voltage regulation mode while the remaining converters operate in over-voltage protection mode. A problem with parallel-input and series-output connected converters is that the output voltages are not all tied to ground, and hence the converter output voltages cannot be directly used by controllers to separately and precisely regulate each of the converters. A problem with existing parallel-input and series-output converters power system is the inability to precisely control the proper distribution of power. Without precise power distribution among the converters, voltage output regulation is degraded and undesirable uneven input current sharing and power distribution can result. Subsequently, undesirable interactions among interconnected converters may exist and can result in regulation instability as well as overstress in one or more of the parallel-input and series-output connected converters. One problem of parallel-input and series-output power systems using multiple converters is the output voltage of each converter is not the same, and hence is non-uniform resulting in instability and uneven power distribution, particularly during any transient start-up, step-line, or step-load transients.
Another problem with parallel-input and series-output connected converter power systems is the lack of a properly unified control for uniform or proportional output voltage distribution for precise distribution of control signals to the converters so as to meet the control objectives for the system, such as, system output voltage protection and system input current-limiting while actively sustaining uniform or proportional output voltages of the converters at all times. The lack of proper control for proportional power distribution among non-identical parallel-input and series-output DC-to-DC converters and proportional-to-power output-voltage limits the use of a mix of converters that have different output voltage and power ratings in a parallel-input and series-output power system. These and other disadvantages are solved or reduced using the invention.